food for thought - swift 5 released - bottom types, string interpolation, and stuff.

[aliak]

I personally love swift as a language because it's just a 
pleasure to write _and_ read. Swift 5 was released recently [0] 
and has a few interesting additions, particularly the additions 
they've added to string interpolation [1] so that you could do 
things like

let a: MyType = "this is an \(type: .interpolated) string"

The "this is a" part is parsed separately by 'a' and the 
interpolated part "\(min: 1) is parsed as a type that is expected 
by your StringInterpolation implementation

// member function that implements string interpolation
mutating func appendInterpolation(min: Int) {
   //...
}

And then as is usual with swift, they try and make it as readable 
as easy to reason with as possible, so they added things like 
isOdd, isEven, and isMultiple(of:) [2] so that you don' t have to 
mentally parse something like "% x == 0" or any bit operation 
magic that tries to be too clever to do the same thing.

And another cool thing was they took their bottom type and made 
it conform to a hashable and equatable type [3]. It would be the 
equivalent if D had an Expect(SuccessType, ErrorType) type and if 
either success or error type could never happen, could be 
replaced by Bottom:

alias NeverError(SuccessType) = Expect!(SuccessType, bottom_t);
alias NeverSuccess(ErrorType) = Expect!(bottom_t, ErrorType);

[0] https://swift.org/blog/swift-5-released/
[1] 
https://github.com/apple/swift-evolution/blob/master/proposals/0228-fix-expressiblebystringinterpolation.md
[2] 
https://github.com/apple/swift-evolution/blob/master/proposals/0225-binaryinteger-iseven-isodd-ismultiple.md
[3] 
https://github.com/apple/swift-evolution/blob/master/proposals/0215-conform-never-to-hashable-and-equatable.md

Cheers,
- Ali